// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 2009-2010 Gael Guennebaud <gael.guennebaud@inria.fr>
// Copyright (C) 2009-2010 Benoit Jacob <jacob.benoit.1@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.

#ifndef EIGEN_RETURNBYVALUE_H
#define EIGEN_RETURNBYVALUE_H

namespace Eigen {

namespace internal {

    template <typename Derived> struct traits<ReturnByValue<Derived>> : public traits<typename traits<Derived>::ReturnType>
    {
        enum
        {
            // We're disabling the DirectAccess because e.g. the constructor of
            // the Block-with-DirectAccess expression requires to have a coeffRef method.
            // Also, we don't want to have to implement the stride stuff.
            Flags = (traits<typename traits<Derived>::ReturnType>::Flags | EvalBeforeNestingBit) & ~DirectAccessBit
        };
    };

    /* The ReturnByValue object doesn't even have a coeff() method.
 * So the only way that nesting it in an expression can work, is by evaluating it into a plain matrix.
 * So internal::nested always gives the plain return matrix type.
 *
 * FIXME: I don't understand why we need this specialization: isn't this taken care of by the EvalBeforeNestingBit ??
 * Answer: EvalBeforeNestingBit should be deprecated since we have the evaluators
 */
    template <typename Derived, int n, typename PlainObject> struct nested_eval<ReturnByValue<Derived>, n, PlainObject>
    {
        typedef typename traits<Derived>::ReturnType type;
    };

}  // end namespace internal

/** \class ReturnByValue
  * \ingroup Core_Module
  *
  */
template <typename Derived> class ReturnByValue : public internal::dense_xpr_base<ReturnByValue<Derived>>::type, internal::no_assignment_operator
{
public:
    typedef typename internal::traits<Derived>::ReturnType ReturnType;

    typedef typename internal::dense_xpr_base<ReturnByValue>::type Base;
    EIGEN_DENSE_PUBLIC_INTERFACE(ReturnByValue)

    template <typename Dest> EIGEN_DEVICE_FUNC inline void evalTo(Dest& dst) const { static_cast<const Derived*>(this)->evalTo(dst); }
    EIGEN_DEVICE_FUNC EIGEN_CONSTEXPR inline Index rows() const EIGEN_NOEXCEPT { return static_cast<const Derived*>(this)->rows(); }
    EIGEN_DEVICE_FUNC EIGEN_CONSTEXPR inline Index cols() const EIGEN_NOEXCEPT { return static_cast<const Derived*>(this)->cols(); }

#ifndef EIGEN_PARSED_BY_DOXYGEN
#define Unusable YOU_ARE_TRYING_TO_ACCESS_A_SINGLE_COEFFICIENT_IN_A_SPECIAL_EXPRESSION_WHERE_THAT_IS_NOT_ALLOWED_BECAUSE_THAT_WOULD_BE_INEFFICIENT
    class Unusable
    {
        Unusable(const Unusable&) {}
        Unusable& operator=(const Unusable&) { return *this; }
    };
    const Unusable& coeff(Index) const { return *reinterpret_cast<const Unusable*>(this); }
    const Unusable& coeff(Index, Index) const { return *reinterpret_cast<const Unusable*>(this); }
    Unusable& coeffRef(Index) { return *reinterpret_cast<Unusable*>(this); }
    Unusable& coeffRef(Index, Index) { return *reinterpret_cast<Unusable*>(this); }
#undef Unusable
#endif
};

template <typename Derived> template <typename OtherDerived> EIGEN_DEVICE_FUNC Derived& DenseBase<Derived>::operator=(const ReturnByValue<OtherDerived>& other)
{
    other.evalTo(derived());
    return derived();
}

namespace internal {

    // Expression is evaluated in a temporary; default implementation of Assignment is bypassed so that
    // when a ReturnByValue expression is assigned, the evaluator is not constructed.
    // TODO: Finalize port to new regime; ReturnByValue should not exist in the expression world

    template <typename Derived> struct evaluator<ReturnByValue<Derived>> : public evaluator<typename internal::traits<Derived>::ReturnType>
    {
        typedef ReturnByValue<Derived> XprType;
        typedef typename internal::traits<Derived>::ReturnType PlainObject;
        typedef evaluator<PlainObject> Base;

        EIGEN_DEVICE_FUNC explicit evaluator(const XprType& xpr) : m_result(xpr.rows(), xpr.cols())
        {
            ::new (static_cast<Base*>(this)) Base(m_result);
            xpr.evalTo(m_result);
        }

    protected:
        PlainObject m_result;
    };

}  // end namespace internal

}  // end namespace Eigen

#endif  // EIGEN_RETURNBYVALUE_H
